Color measurement instruments for many and varied applications are well known. These instruments are used, for example, to determine color consistency in printed material, photographic material, textiles, and plastics. The most comprehensive color measurements are obtained by instruments known as spectrophotometers, which measure the spectral distribution of light and give a percentage reflection or transmission at many segments in the visible color spectrum.
The field of desk top publishing has expanded greatly in recent years, and color output devices such as color printers, plotters, proofers have become widely used. The color output devices are often controlled by computer software, which transmits control signals to the printer defining color to be produced. To assure color quality, it is desirable to be able to calibrate color printers to produce a selected quality of color for printed material produced by a number of different printers. Additionally, data defining a color product may be transmitted to remote locations to be printed by a variety of printers. In order to be able to provide a product of consistent color characteristics, a comparison to a color standard is required. All of these functions require the accurate measurement of many samples of different colors produced on the device. These colors are produced using only a few colorants--usually cyan (C), magenta (M), yellow (Y), and black (K).
A color measurement instrument, such as a spectrophotometer, includes a color measurement engine having an optical pick-up. Additionally, many instruments include a drive mechanism for moving either the sample or the engine to effect relative movement between the two. The registration of the sample with respect to the engine and the controlled movement of the sample or the engine are critical components in obtaining consistent and accurate measurements. Only small changes in the distance between the sample and the measurement engine can create significant errors and inconsistencies in the color measurement.
Prior color measurement instruments are illustrated in U.S. Pat. No. 5,369,494 issued Nov. 29, 1994 and entitled "Portable Scanning Colorimeter"; U.S. Pat. No. 5,118,183 issued Jun. 2, 1992 and entitled "Automated Strip Reader Densitometer"; and U.S. Pat. No. 5,062,714 issued Nov. 5, 1991 and entitled "Apparatus and Method for Pattern Recognition." In these units, the sample drive mechanism is located in the base, while the color measurement engine is located in an assembly above the base. Because these two primary components are located in different housings, there is the possibility that sample registration and movement is not as precisely controlled as required for present day measurement. Accordingly, artisans continue to seek improved structures for maintaining improved consistency and accuracy in sample registration and movement.